I'm not doing Nano, but have you tried good ol' pen and paper? Sometimes when I'm tired of sitting in front of my computer typing I like to step away and write down the story for awhile. Which usually lasts until the thoughts come to fast for me to write and I need to go type them down.

Also, like the above suggested, reading, watching TV, knitting, et cetra. Anything to just get away from the computer for an hour or two before going back to it.